Per Baseball America, MLB and AAA spring training will start on time, then the rest of the minor leagues later. That would mean a delay in the minor league season below AAA until at least May.
https://nationalsprospects.com/2021/01/milb-delayed-below-aaa-for-2021/This, of course, presuming that MLB and AAA start on time in about six weeks. With a late March/early April start, that would have the minors beginning in May.
While the season may be pushed into September/October, it will reportedly be at the expense of playoffs. To reduce travel, it would appear that the schedule will be six days on, one day off. Essentially, homestands (if/when fans are allowed to attend) will be every other week.
As BA noted, players and operators will both actually like this arrangement. The former because even a day with travel, which you can probably bank on being optimized for as short a trip as possible between stops, they’re not playing at least once a week vs. once or twice a month. The latter will like it because homestands will be limited to six days at a time and every homestand will have weekend games.